1. Field of the Invention
The present invention generally relates to medical devices, and more specifically relates to valve assemblies for implantable prostheses and tissue expanders.
2. Description of the Related Art
Implantable prostheses are commonly used to replace or augment body tissue. In instances of breast cancer, it may be necessary to remove some or all of the mammary gland and surrounding tissue. This surgery leaves a void that can be filled with an implantable prosthesis that supports surrounding tissue and provides a normal body appearance, eliminating much of the shock and depression that often follows breast cancer surgeries. Implantable prostheses may also used for breast augmentation procedures.
Tissue expanders are implantable devices that are placed beneath the skin and then gradually inflated to stretch the overlying tissue. Tissue expanders are commonly used to create a pocket for receiving a permanent prosthesis or to generate an increased skin surface area in anticipation of utilizing the newly grown skin for grafting or reconstruction procedures. After implantation, a solution, such as a saline solution, is periodically injected into the tissue expander to increase the volume of the tissue expander. Between injections, the surrounding skin is permitted to stretch and grow to create the increased skin surface. The solution may also be withdrawn from the tissue expander to reduce the internal volume and size of the expander.
Implantable prostheses and tissue expanders typically have a silicone shell that is manufactured by dipping an appropriately sized and shaped mandrel into a biocompatible silicone elastomer. Once the silicone shell has been formed, it is removed from the mandrel. The dip-molding process results in the formation of a silicone shell having a mandrel opening, e.g., a circular hole, in one of its faces. The mandrel opening is subsequently covered with a patch that seals the mandrel opening to form a fluid impervious implant shell. The patch may be attached to the implant shell using silicone rubber or other similar biocompatible adhesives. The completed shell can remain unfilled, be pre-filled, or intraoperatively filled through a small fill port or valve with a solution, such as saline solution, gel, foam, or combinations of these materials.
In many instances, implantable prostheses and tissue expanders have valves that allow medical personnel to add and remove fluid for adjusting the size of the devices. The valves used in these implants tend to be large and palpable. Permanent implants, e.g., breast implants, have filling tubes which may be used to add and withdraw fluid, however, these implants typically do not allow for adjustment of the implant after the filling tube is removed. As such, the pathway left after withdrawal of the filling tube is permanently closed.
There have been many efforts directed to providing valves for implants. U.S. Pat. No. 4,263,682 discloses a self-sealing valve for a fluid fillable implant, such as a mammary prosthesis, having first and second planar members that are bonded together in such a manner that leaves a bonded region and an elongated, unbonded region therebetween. Openings are formed in the planar members of the valve to provide for communication between the unbonded region and the inside and outside of the valve. The openings are offset from one another so that the openings in the unbonded region form a normally open channel through the valve. At least one of the planar members is sufficiently flexible to close the normally open channel in response to fluid pressure from within a fluid filled implant. Unfortunately, in use, it has been observed that the interior fluid pressure is not sufficient to prevent the leakage of fluid through the valve.
U.S. Pat. No. 3,600,718 to Boone discloses an inflatable prosthesis having an inflatable shell and a filling stem for introducing a filling fluid to inflate the shell. At the point of introduction of the filling stem, there is provided a capsule of sealing gel through which the stem passes. After implantation and inflation, the stem is withdrawn, either wholly or partially, and the gel in the capsule seals the stem outlet against leakage from the inflating fluid.
U.S. Pat. No. 5,019,101 to Purkait et al. discloses an implantable device having a self-sealing valve including a main body portion having a channel for receiving a fill tube. The valve includes a gel-filled chamber in which the main body portion thereof is disposed. The main body portion has a free end that is occluded by the gel once the fill tube has been withdrawn from the fill tube chamber.
In spite of the above advances, there remains a need for prosthetic implants and tissue expanders having valve assemblies that are highly leak resistant and that facilitate adding and removing solution from the implant shell. There also remains a need for prosthetic implants and tissue expanders having valve assemblies that enable solution to be easily added and removed both before and after implantation. In addition, there remains a need for implants and tissue expanders having valve assemblies having a low profile, and that are minimally palpable.